In a vehicle such as an automobile and the like, an airbag is installed in preparation for an eventual collision. The airbag inflates and expands to restrict an occupant upon collision and enables the impact applied to the occupant to be reduced.
Well known airbags are a driver seat airbag and a passenger seat airbag, which are mounted in a steering wheel and a dashboard to restrict the occupants on a driver seat and a passenger seat upon a head-on collision and to reduce the impact applied to the occupants, respectively.
An airbag is normally used together with a seatbelt as an apparatus for restricting an occupant upon collision of a vehicle. The motion of an occupant upon collision varies depending on whether or not the occupant wears a seatbelt. Then, it is proposed to change the expansion mode of an airbag depending on whether or not a seatbelt is worn (for example, refer to Japanese Unexamined Patent Application Publication No. 2000-43672).
As a method of changing the expansion mode of an airbag, for example, there is a method such that a vent hole provided in a bag is closed in an early stage of expansion and is then opened (U.S. Patent Application Publication No. 2003/0020266). There is also a method such that a vent hole provided in a bag is opened in an early stage of expansion and is then closed (U.S. Patent Application Publication No. 2004/0012179). Moreover, there is a method such that expansion size can be changed in plural steps (U.S. Patent Application Publication No. 2004/0012179). In these airbags, gas discharge characteristics are controlled depending on the position and size of an occupant and a state of using a seatbelt.
In addition, the following arts are proposed as attempts to optimize the expansion of an airbag. In Japanese Unexamined Patent Application Publication No. H07-186879, the quantity of gas discharged from an airbag is adjusted depending on the weight and position of a vehicle occupant, and the pressure of the airbag at vehicle collision is controlled. In Japanese Unexamined Patent Application Publication No. 2000-142309, the position of an occupant is detected, and the displacement of the occupant is predicted from an acceleration signal of a collision sensor. And an airbag is expanded based on the predicted displacement.
In Japanese Unexamined Patent Application Publication No. H11-310098, it is described that an opening degree of a gas outlet of an airbag is favorably conformed according to each of occupants. A cross-sectional area of the gas outlet remains unchanged during restricting operation. Instead of that, the cross-sectional area is optimized with respect to the respective occupants at the time before the airbag expands. In Japanese Unexamined Patent Application Publication No. H10-35405, it is described that a controller controls an opening degree of a pressure reducing hole so that the gas pressure for expanding an airbag is always within a normal range even when a gas generator is activated under any temperature condition.
In Japanese Unexamined Patent Application Publication No. 2000-43672, whether or not a discharge port is to be opened is limited to whether or not the seatbelt is worn, so the expansion (release) mode of the airbag is not changed because of occupant weight, collision speed, or the like. Furthermore, being also common to U.S. Patent Application Publication No. 2003/0020266, since the quantity of discharged gas is small in an early stage of expansion and becomes large in a late stage, there is a possibility that the force applied to an occupant becomes large depending on collision speed.
In the case of U.S. Patent Application Publication No. 2004/0012179, thickness restricting control and vent-hole opening degree control are separately constructed and still are concurrently operated; therefore, the structure is complicated. Moreover, since adaptive vents are disposed at two places, the number of manufacturing man-hours is large.
In conventional methods of adjusting airbag expansion, although intended to conform to occupant status, airbag expansion and gas discharge characteristics are not controlled depending on a collision situation. On this account, it is necessary to reduce the force applied to a nearby occupant.